1. Field of the Invention
The present invention relates to a thin film magnetic head to be used for a floating type magnetic head. More particularly, the present invention relates to a thin film magnetic head that can properly reduce side-fringing and improve overwrite.
2. Description of the Related Art
FIG. 13 is a partial front view of the structure of a conventional thin film magnetic head (an inductive head) viewed from the surface side facing a recording medium. The reference numeral 1 shown in FIG. 13 is a lower core layer formed of a magnetic material such as Permalloy.
As shown in FIG. 13, a lower magnetic pole layer 3, a gap layer 5 and an upper magnetic pole layer 6 are formed on the lower core layer 1, and the width of the upper pole layer 6 in the track width direction (the X direction in the drawing) is restricted to have a track width Tw.
The lower magnetic pole layer 3, gap layer 5 and upper magnetic pole layer 6 are formed so as to be exposed on a surface facing the recording medium.
Insulation layers 7 are formed at both sides of the lower magnetic pole layer 3, gap layer 5 and upper magnetic pole layer 6 along the track width direction (X direction) as shown in FIG. 13.
A coil layer 13 (not shown) is formed at the back of the insulation layers 7 in the height direction (the Y direction in the drawing).
A magnetically coupled upper core layer 8 is formed on the upper magnetic pole layer 6 as shown in FIG. 13. The tip surface of the upper core layer 8 is formed so as to be exposed on the surface facing the recording medium as shown in FIG. 13, and the width T3 of the upper core layer 8 in the track width direction is formed to be larger than the track width Tw.
However, the structure of the conventional thin film magnetic head involved the following problems.
The upper magnetic pole layer 6 and the upper core layer 8 were formed of magnetic materials having the same saturation magnetic flux densities Bs with each other in the conventional thin film magnetic head. Accordingly, as shown in FIG. 13, the leak magnetic field generated from the upper core layer 8 formed with a width T3 larger than the track width Tw in the upper magnetic pole layer 6 did not concentrate in the vicinity of the gap layer, and the leak magnetic field was generated to spread toward the track width direction with a width larger than the track width Tw (the arrow shown by dotted arrows in FIG. 13), thereby causing side-fringing.
Side-fringing would be more evident when the track width Tw is further reduced for increasing the recording density in the future.
One method devised for suppressing side-fringing from generating is, for example, to form the tip surface 8a of the upper core layer 8 directed toward the surface side facing the recording medium so that it is retreated toward the height direction (Y direction) from the surface facing the recording medium.
When the upper core layer 8 and the upper magnetic pole layer 6 are formed of the magnetic materials having the same saturation magnetic flux densities with each other, the retreat length (the recess length) should be increased for properly preventing side-fringing from generating. However, it is a problem that the contact area between the upper magnetic pole layer 6 and the upper core layer 8 as well as overwrite decrease. Overwriting as used herein refers to writing the signals over the signals that have been already recorded. Signals are at first recorded at a low frequency, and then overwritten at a high frequency. The overwrite is accessed by the amount of decrease of remanent output of the recording signal from the recording signal output at the low frequency before high frequency overwriting.
Accordingly, it is an object of the present invention for solving the foregoing problems to provide a thin film magnetic head capable of properly preventing side-fringe from generating while improving the overwrite.
The present invention provides a thin film magnetic head comprising a lower core layer, a recording core, an upper core layer formed on the recording core, and a coil for inducing a recording magnetic field on the lower core layer, recording core and upper core layer; with the recording core comprising a lower magnetic pole layer, a gap layer and an upper magnetic pole layer, or a gap layer and an upper magnetic pole layer, sequentially laminated on the lower core layer, and exposed on a surface facing a recording medium, and wherein the upper magnetic pole layer is formed of a magnetic material having a higher saturation magnetic flux density than the upper core layer, and the upper core layer is directly bonded to the upper magnetic pole layer.
The upper magnetic pole layer has a higher saturation magnetic flux density than the upper core layer in the present invention. The upper core layer having a higher saturation magnetic flux density than the saturation magnetic flux density of the upper magnetic pole layer is directly bonded on the upper magnetic pole layer. Consequently, the leak magnetic field generated from the upper core layer may concentrate in the vicinity of the gap layer to hardly spread the leak magnetic field in the track width direction with a width wider than the track width Tw, thereby enabling side-fringing to be properly suppressed from generating.
Since the saturation magnetic flux density Bs1 of the upper magnetic pole layer is higher than the saturation magnetic flux density Bs2 of the upper core layer in the present invention, magnetic saturation in the upper magnetic pole layer, and thus attenuation of the magnetic flux density, may be suppressed to enable the overwrite to be improved.
Preferably, the ratio Bs1/Bs2 between the saturation magnetic flux density Bs1 of the upper magnetic pole layer and the saturation magnetic flux density Bs2 of the upper core layer is 1.08 or more, because side-fringing is suppressed while improving the overwrite when the ratio is within the range as described above.
Preferably, the saturation magnetic flux density Bs1 of the upper magnetic pole layer is 1.3 T or more, and the saturation magnetic flux density Bs2 of the upper core layer is 1.2 T or less.
It is preferable that the tip surface of the upper core layer directing toward the side facing the recording medium is located at a certain distance retreat from the surface facing the recording medium to the height direction, because side-fringing may be properly suppressed by the disposition of the tip surface as described above.
Although the overwrite decreases due to decrease of the contact area between the upper magnetic pole layer and upper core layer when the retreat distance is too large, the magnitude of generated side-fringing is not so large in the present invention even when the tip surface of the upper core layer is exposed on the surface facing the recording medium. Accordingly, generation of side-fringing can be more properly suppressed with a small retreat distance of the tip surface, thereby enabling a high OR intensity to be maintained without causing a decrease in the contact area between the upper core layer and upper magnetic pole layer.
Preferably, the shortest retreat distance L1 from the surface facing the recording medium to the tip surface of the upper core layer is within a range of 0 less than L1xe2x89xa61.5 xcexcm, because good OR intensity may be maintained without decreasing the contact area between the upper core layer and upper magnetic pole layer.